Re: [libvirt] [PATCH] qemu: hyperv: Add enlightenment support for TSC timekeeping
On Tue, 2014-02-04 at 16:04 +0100, Peter Krempa wrote:
[adding Vadim as he implemented the qemu/kvm parts]
On 01/22/14 11:35, Daniel P. Berrange wrote:
On Tue, Jan 21, 2014 at 06:54:34PM +0100, Peter Krempa wrote:
The hyperv enlightenment features allow to ease guests timekeeping by
allowing to store offset from the TSC as a reference. Add the support
for enabling this flag in qemu.
I'm not sure I entirely understand what this is doing with TSC, but
we do have a generic timer element for controlling various attributes
of platform timers. I can't help thinking it'd be better to keep this
TSC related setting there instead
This functionality provides hypercalls defined by the Microsoft's
enlightenment standards. These provide calibration data and actual
values that can be used by the guest to calculate time. [1]
The actual implementation uses data provided by the kvmclock code:
+ case HV_X64_MSR_TIME_REF_COUNT: {
+ data =
+ div_u64(get_kernel_ns() + kvm-arch.kvmclock_offset, 100);
+ break;
+ }
along with a few values that will allow the guest to use the data.
Technically this is a new timer for VM's running windows and as with
kvmclock, cpu features are used to show the availability of this feature
to the guest.
There is yet another enlightenment option for windows guests that run
on platforms that support the invariant TSC (iTSC). This option will add
hypercall to retrieve calibration data so that the host processors iTSC
will be used as the timing source eliminating the need to read the timer
value via a hypercall.
Technically, it is not a hypercall, just a normal call RDTSC, but then
kernel normalizes the returned value to 10MHz and adds offset. Kernel
(KVM) shares scale and offset date with a guest through a dedicated page
allocated by guest. We have pretty good working prototype at the moment,
but this part has not been committed to upstream yet.
Best regards,
Vadim.
I agree on your idea of moving this option into the timer section. How
about naming it timer name=hv-rtc ?
Daniel
Peter
[1]:
http://msdn.microsoft.com/en-us/library/windows/hardware/ff542637(v=vs.85).aspx
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Re: [libvirt] [PATCH] qemu: hyperv: Add enlightenment support for TSC timekeeping
[adding Vadim as he implemented the qemu/kvm parts]
On 01/22/14 11:35, Daniel P. Berrange wrote:
On Tue, Jan 21, 2014 at 06:54:34PM +0100, Peter Krempa wrote:
The hyperv enlightenment features allow to ease guests timekeeping by
allowing to store offset from the TSC as a reference. Add the support
for enabling this flag in qemu.
I'm not sure I entirely understand what this is doing with TSC, but
we do have a generic timer element for controlling various attributes
of platform timers. I can't help thinking it'd be better to keep this
TSC related setting there instead
This functionality provides hypercalls defined by the Microsoft's
enlightenment standards. These provide calibration data and actual
values that can be used by the guest to calculate time. [1]
The actual implementation uses data provided by the kvmclock code:
+ case HV_X64_MSR_TIME_REF_COUNT: {
+ data =
+div_u64(get_kernel_ns() + kvm-arch.kvmclock_offset, 100);
+ break;
+ }
along with a few values that will allow the guest to use the data.
Technically this is a new timer for VM's running windows and as with
kvmclock, cpu features are used to show the availability of this feature
to the guest.
There is yet another enlightenment option for windows guests that run
on platforms that support the invariant TSC (iTSC). This option will add
hypercall to retrieve calibration data so that the host processors iTSC
will be used as the timing source eliminating the need to read the timer
value via a hypercall.
I agree on your idea of moving this option into the timer section. How
about naming it timer name=hv-rtc ?
Daniel
Peter
[1]:
http://msdn.microsoft.com/en-us/library/windows/hardware/ff542637(v=vs.85).aspx
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Re: [libvirt] [PATCH] qemu: hyperv: Add enlightenment support for TSC timekeeping
On Tue, Feb 04, 2014 at 04:04:06PM +0100, Peter Krempa wrote:
[adding Vadim as he implemented the qemu/kvm parts]
On 01/22/14 11:35, Daniel P. Berrange wrote:
On Tue, Jan 21, 2014 at 06:54:34PM +0100, Peter Krempa wrote:
The hyperv enlightenment features allow to ease guests timekeeping by
allowing to store offset from the TSC as a reference. Add the support
for enabling this flag in qemu.
I'm not sure I entirely understand what this is doing with TSC, but
we do have a generic timer element for controlling various attributes
of platform timers. I can't help thinking it'd be better to keep this
TSC related setting there instead
This functionality provides hypercalls defined by the Microsoft's
enlightenment standards. These provide calibration data and actual
values that can be used by the guest to calculate time. [1]
The actual implementation uses data provided by the kvmclock code:
+ case HV_X64_MSR_TIME_REF_COUNT: {
+ data =
+ div_u64(get_kernel_ns() + kvm-arch.kvmclock_offset, 100);
+ break;
+ }
along with a few values that will allow the guest to use the data.
Technically this is a new timer for VM's running windows and as with
kvmclock, cpu features are used to show the availability of this feature
to the guest.
There is yet another enlightenment option for windows guests that run
on platforms that support the invariant TSC (iTSC). This option will add
hypercall to retrieve calibration data so that the host processors iTSC
will be used as the timing source eliminating the need to read the timer
value via a hypercall.
I agree on your idea of moving this option into the timer section. How
about naming it timer name=hv-rtc ?
Sounds reasonable, or hyperv-rtc since 'hv' can be misinterpreted to
just mean 'hypervisor'
Daniel
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Re: [libvirt] [PATCH] qemu: hyperv: Add enlightenment support for TSC timekeeping
On Tue, Jan 21, 2014 at 06:54:34PM +0100, Peter Krempa wrote: The hyperv enlightenment features allow to ease guests timekeeping by allowing to store offset from the TSC as a reference. Add the support for enabling this flag in qemu. I'm not sure I entirely understand what this is doing with TSC, but we do have a generic timer element for controlling various attributes of platform timers. I can't help thinking it'd be better to keep this TSC related setting there instead Daniel -- |: http://berrange.com -o-http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :| -- libvir-list mailing list libvir-list@redhat.com https://www.redhat.com/mailman/listinfo/libvir-list
Re: [libvirt] [PATCH] qemu: hyperv: Add enlightenment support for TSC timekeeping
On 01/21/2014 10:54 AM, Peter Krempa wrote: The hyperv enlightenment features allow to ease guests timekeeping by allowing to store offset from the TSC as a reference. Add the support for enabling this flag in qemu. --- Notes: This feature is still under development in qemu. I will wait until it's finished before pushing this: http://lists.nongnu.org/archive/html/qemu-devel/2014-01/msg02569.html Looks okay code-wise, but I agree with holding off in libvirt.git until after the qemu.git commit id is known. -- Eric Blake eblake redhat com+1-919-301-3266 Libvirt virtualization library http://libvirt.org signature.asc Description: OpenPGP digital signature -- libvir-list mailing list libvir-list@redhat.com https://www.redhat.com/mailman/listinfo/libvir-list
